Guided is best i think. We did a bit in Talland Bay the other week and enjoyed it.
Probably Ibizakayak unless you want to muck about trying to rent a clear perspex one in Pou d'es Lleo from the guy who keeps double-booking and canceling stuff at the last minute !
Ibizakayak : http://www.ibizakayak.es/english/ +34 687 09 18 10
Run by the utterly bonkers (and hilarious) Viking of Ibiza that is Martina Greef